The invention relates to a device for retaining a prosthesis element on an osseous segment or part, in particular to a dental prosthesis, which can be fitted in removable manner on the jawbone.
The conventional mechanical devices for retaining a prosthesis element on an osseous segment, using such as cuppings, springs or special geometries, besides occasionally causing painful pressures on the mucous membrane, are not very effective and are poorly tolerated.
The fixation of prosthetic retaining implants in bone foundation of the jawbone has already been proposed. Such a technique, however, entails passing through the mucous membrane and maintaining the fixing components in position which may cause microbial infections and the irreversible destruction of the osseous foundation.
A recent solution offering many advantages consists in retaining the prosthetic element by magnetic forces generated by one or several magnetic systems each including a magnetic or magnetizable material implanted internally in a cavity made in the bone foundation and of a magnetic or magnetizable material contained externally in the prosthetic element. Hereafter, a magnetic material, whether used internally or externally, will denote a magnetic as well as a magnetizable element in each magnetic system, at least one of the elements being a true magnet.
The object of the present invention consists in improvements in the magnetic material contained externally in the prosthetic element as regards its structure, its assembly and its retaining means.
The co-pending U.S. Patent application Ser. No. 772,999, filed Feb. 28, 1977 in the name of the same inventor discloses how to associate a base structure, to be located in the clearance cavity made in the osseous segment, with the internal magnetic material, means furthermore being provided to lock the base structure in the clearance cavity once it has been inserted into it, and also means being provided to retain, preferably in removable manner, the magnetic material on the base structure.
In this fashion, the position of the internal magnetic material is entirely determined.
It is, however, required that the magnitude of the magnetic force generated by the interaction of the two magnetic materials correspond perfectly to the requirement at hand, i.e., achieving sufficient but not excessive retention, so as to avoid unbearable compression of the mucous membrane.
As already stated, the retention of the internal magnetic material on its base structure preferably is implemented in a removable manner, and in theory, at least, one may try successively several magnetic elements of different strengths in order to obtain the precisely fitting magnetic force required. However, each new effort would require another manipulation and this would rapidly become intolerable to the patient. The ability to remove the internal material is justified only in view of a possible ultimate loss of magnetic power of said material which then would have to be replaced.
Accordingly, elements preferably are so selected that the retention of the prosthesis is reliably obtained, and preferably means are provided to adjust the magnitude of the air gap, or other gap between the magnetic pole faces, to keep the compression on the mucous membrane within reasonable limits. Furthermore, the magnetic field seeks its own maximum, that is, the magnetic forces tend to so displace the two conjugate magnetic materials that their axes will tend to coincide, and therefore, the position of the external magnetic material can be adjusted to be in a plane parallel to that of the front face of the internal material, whereby the prosthesis will rest on the jawbone only very lightly outside the periods of use (for instance when chewing). Not only does the magnetic field provide for the retention of the prosthesis, but furthermore, it acts as a permanent and stable shock absorber.
One object of the invention is to ensure that the external magnetic material is rigidly mounted to a support, itself fixed in a frame fastened to the prosthesis and housed in the latter's thickness, means being provided to adjust--preferably in continuous manner--the relative position of the support in the frame, on one hand in a plane parallel to that of the front face of the internal material so as to adjust the relative position of the axes of the internal and external magnetic materials, and on the other hand, in a direction perpendicular to this plane so as to adjust the gap between the magnetic poles.